Paraffin wax

Paraffin wax is a white or colorless soft solid derivable from petroleum, coal or oil shale, that consists of a mixture of hydrocarbon molecules containing between twenty and forty carbon atoms. It is solid at room temperature and begins to melt above approximately 37 °C (99 °F);[1] its boiling point is >370 °C (698 °F).[2] Common applications for paraffin wax include lubrication, electrical insulation, and candles. [3] It is distinct from kerosene, another petroleum product that is sometimes called paraffin.

In chemistry, paraffin is used synonymously with alkane, indicating hydrocarbons with the general formula CnH2n+2. The name is derived from Latinparum ("barely") + affinis, meaning "lacking affinity" or "lacking reactivity", referring to paraffin's unreactive nature.[4]

Contents

Paraffin wax is mostly found as a white, odorless, tasteless, waxy solid, with a typical melting point between about 46 and 68 °C (115 and 154 °F),[5] and a density of around 900 kg/m3.[6] It is insoluble in water, but soluble in ether, benzene, and certain esters. Paraffin is unaffected by most common chemical reagents but burns readily.[7] Its heat of combustion is 42 kJ/g.

Paraffin wax is an excellent material for storing heat, with a specific heat capacity of 2.14–2.9 J g−1 K−1 (joules per gramkelvin) and a heat of fusion of 200–220 J g−1.[11] This property is exploited in modified drywall for home building material: a certain type of wax (with the right melting point) is infused in the drywall during manufacture so that it melts during the day, absorbing heat, and solidifies again at night, releasing the heat.[12] Paraffin wax phase-change cooling coupled with retractable radiators was used to cool the electronics of the Lunar Rover.[13] Wax expands considerably when it melts and this allows its use in wax thermostatic elementthermostats for industrial, domestic and, particularly, automobile purposes.[14][15]

The feedstock for paraffin is slack wax, which is a mixture of oil and wax, a byproduct from the refining of lubricating oil.

The first step in making paraffin wax is to remove the oil (de-oiling or de-waxing) from the slack wax. The oil is separated through crystallization. Most commonly, the slack wax is heated, mixed with one or more solvents such as a ketone and then cooled. As it is cooled, wax crystallizes out leaving oil in solution. This mixture is filtered into two streams: solid (wax plus some solvent) and liquid (oil and solvent). After the solvent is recovered by distillation, the resulting products are called "product wax" (or "press wax") and "foots oil". The lower the percentage of oil in the wax the more refined it is considered (semi-refined versus fully refined).[16] The product wax may be further processed to remove colors and odors. The wax may finally be blended together to give certain desired properties such as melt point and penetration. Paraffin wax is sold in either liquid or solid form.[17][18][19]

In industrial applications, it is often useful to modify the crystal properties of the paraffin wax, typically by adding branching to the existing carbon backbone chain. The modification is usually done with additives, such as EVA copolymers, microcrystalline wax, or forms of polyethylene. The branched properties result in a modified paraffin with a higher viscosity, smaller crystalline structure, and modified functional properties. Pure paraffin wax is rarely used for carving original models for casting metal and other materials in the lost wax process, as it is relatively brittle at room temperature and presents the risks of chipping and breakage when worked. Soft and pliable waxes, like beeswax, may be preferred for such sculpture, but "investment casting waxes," often paraffin-based, are expressly formulated for the purpose.

In a pathology laboratory, paraffin wax is used to impregnate tissue prior to sectioning thin samples of tissue. Water is removed from tissue through ascending strengths of alcohol (75% to absolute) and the tissue is cleared in an organic solvent such as xylene. The tissue is then placed in paraffin wax for a number of hours and then set in a mold with wax to cool and solidify; sections are cut then on a microtome.

Forensic investigations: the nitrate test uses paraffin wax to detect nitrates and nitrites on the hand of a shooting suspect

Antiozonant agents: blends of paraffin and micro waxes are used in rubber compounds to prevent cracking of the rubber; the admixture of wax migrates to the surface of the product and forms a protective layer. The layer can also act as a release agent, helping the product separate from its mould.[22]

Mechanical thermostats and actuators, as an expansion medium for activating such devices[15]

"Potting" guitar pickups, which reduces microphonic feedback caused from the subtle movements of the pole pieces

"Potting" of local oscillator coils to prevent microphonic frequency modulation in low end FM radios.

^Nasser, William E (1999). "Waxes, Natural and Synthetic". In McKetta, John J. Encyclopedia of Chemical Processing and Design67. New York: Marcel Dekker. p. 17. ISBN0-8247-2618-9. This can vary widely, even outside the quoted range, according to such factors as oil content and crystalline structure.